The White House is considering at least three troop withdrawal options from Iraq as President Obama has pledged to pull out soldiers in 16 months.

United States military planners have drawn up three options to allow Obama to remove combat troops from Iraq.

The timelines under discussion are 16 months, proposed by Obama as a centerpiece of his presidential campaign, 19 months and 23 months, Reuters quoted a US official as saying, who spoke on the condition of anonymity on Saturday.

Senior US military commanders including US Army generals Ray Odierno, the top US commander in Iraq, and David Petraeus, the head of US Central Command favor the slowest of the three.

“Odierno and Petraeus have said that we really need 23 months to do this without jeopardizing the security gains that we’ve secured,” the official said.

Under either of the timelines, the US would like to leave behind a number of brigades that would be reconfigured as multipurpose units to provide training and advising for Iraqi security forces.

The force is likely to consist of tens of thousands of troops, military officials and analysts say.

These brigades would be considered noncombatant, but their presence would have to be agreed in advance by the Iraqi government, which under a deal signed late last year insisted that all US forces, not just combat brigades, be out of Iraq by the end of 2011.

Obama made opposition to the Iraq war one of his presidential campaign mantras and said that he would withdraw US forces in 16 months, emphasizing Afghanistan and vowing to add significantly to the 36,000-strong US forces there, bringing the number as high as 60,000.

However, the fact that Obama did not immediately order his generals to begin withdrawing after he took office, hints that even before assuming office, he was aware of the dangers of a quick withdrawal.

During Obama’s first meeting with the Joint Chiefs of Staff at the Pentagon last week, he did not mention a 16-month timeline, according to officials who were present.

US commanders have repeatedly cautioned against what they call withdrawing troops from Iraq prematurely, arguing that the country remains fragile.